Solid-state image pickup device and method for driving the same

ABSTRACT

In a solid-state image pickup device, third transfer electrodes are disposed in parallel to vertical transfer registers, and second transfer electrodes are disposed vertically to the vertical transfer registers. These transfer electrodes are also formed on the read-out gate portions to supply a driving voltage for reading out signal charges from photoelectric conversion elements. On the basis of the driving voltage applied to both the third and second transfer electrodes, the read-out of the signal charges to the vertical transfer registers is carried out. At the portion where the read-out of the signal charges is carried out, the transfer electrode at the read-out gate portion side and the sensor area of the photoelectric conversion element are formed so as to be adjacent to each other. At the portion where no read-out of signal charges is carried out, an offset area is provided between the transfer electrode at the read-out gate portion side and the sensor area of the photoelectric conversion element.

RELATED APPLICATION DATA

The present application claims priority to Japanese Application(s)No(s). P2000-377573 filed Dec. 12, 2000, which application(s) is/areincorporated herein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state image pickup devicehaving photoelectric conversion elements (sensors) which are arrangedtwo-dimensionally, such as a CCD solid-state image pickup device, and amethod of driving the solid-state image pickup device.

2. Description of the Related Art

In order to enhance the dynamic range in an image sensor using a CCDsolid-state image pickup device (hereinafter referred to as “CCD imagesensor”), there have been proposed various methods of picking up imageswith photoelectric conversion elements which are different insensitivity and then composing these pickup images into an image.

According to a first method of these methods, incident light isoptically split to plural optical axes which are different intransmittance, and then the light beams thus split are detected byplural CCD image sensors arranged on the respective optical axes (seeJapanese Laid-open Patent Application Nos. Hei-8-223491, Hei-7-254965,Hei-7-254966, Hei-8-340486 and Hei-10-69011, and U.S. Pat. No.5,801,773).

According to a second method, an exposure time is divided into pluralsub exposure times, plural images are respectively picked up at adifferent time and for a different sub exposure time by using one CCDimage sensor, and then the plural images thus achieved are composed withone another (see Japanese Laid-open Patent Application Nos. Hei-8-331461and Hei-7254965, U.S. Pat. Nos. 5,420,635 and 5,455,621, JapaneseLaid-open Patent Application No. Hei-6-141229, U.S. Pat. No. 5,801,773,U.S. Pat. No. 5,638,118 and U.S. Pat. No. 5,309,243).

According to a third method, an image is picked up by using one CCDimage sensor while the photoelectric conversion elements of the CCDimage sensor are made different in sensitivity, and then signalsdetected by the plural photoelectric conversion elements different insensitivity are composed with one another (see U.S. Pat. No. 5,789,737,Japanese Laid-open Patent Application No. Sho-59-217358, U.S. Pat. No.5,420,635). In these prior art publications, it has been proposed thatfilters different in transmittance are covered on the respectivephotoelectric conversion elements as a method of varying the sensitivityof the photoelectric conversion elements in the CCD image sensor.

The first method needs plural CCD image sensors and a complicatedoptical system for splitting light, and thus has a problem that themanufacturing cost and the scale of the apparatus are increased.

According to the second method, information (image) detected withdifferent sensitivity is achieved at a different time and for adifferent sub exposure time, so that it is difficult to accurately pickup the images of a moving subject and the resolution to a moving subject(hereinafter referred to as “dynamic resolution”) cannot be enhanced.

Further, the third method can solve the problems of the first and secondmethods, that is, both the problem that the apparatus is complicated andthe problem that the dynamic resolution cannot be enhanced. However, inthe third method, the filters different in transmittance must be coveredon the photoelectric conversion elements to perform sensitivity control,and thus the sensitivity of each photoelectric conversion element isfixed in the manufacturing process of the CCD image sensor, so that thesensitivity cannot be variably controlled. Therefore, it is difficult tovariably control the enlarging rate of the dynamic range in accordancewith the condition.

In order to avoid the problem that it is difficult to variably controlthe enlargement rate of the dynamic range in accordance with thecondition because the sensitivity of each photoelectric conversionelement is fixed, Japanese Laid-open Patent Application No. Hei-9-191099discloses a technique in which signals of a selected column are read outafter a first accumulation time, then an electrical shutter is actuated,and then signals of columns other than the above selected column areread out after a subsequent second accumulation time, thereby enlargingthe dynamic range.

However, as in the case of the method of covering the photoelectricconversion elements with the filters, the third method has a problemthat the degree of freedom for the design of a spatial pattern ofsensitivity is low, and for example it has a problem that signals havingplural kinds of exposure times such as three or more kinds cannot beachieved in the vertical direction.

Further, since the first accumulation time and the second accumulationtime are timely separated from each other by the charge sweep-outoperation of the electronic shutter, the image pickup timing isdifferent between a column from which charges are read out for the firstaccumulation time and a column from which charges are read out for thesecond accumulation time. Therefore, the dynamic resolution cannot beenhanced like the second method.

Still further, in order to promote the multi-pixel design or the compactdesign for the CCD solid-state image pickup device used for the CCDimage sensor described above, the unit cell of each pixel is required tobe designed in a more minute structure (that is, the microstructure ofthe unit cell is required to be further enhanced).

SUMMARY OF THE INVENTION

In order to solve the above problems, an object of the present inventionis to provide a solid-state image pickup device that brings flexibilityto the spatial pattern design of the sensitivity of each photoelectricconversion element, has a broad dynamic range and a high dynamicresolution and is suitable in structure for further microstructure, anda method of driving the solid-state image pickup device.

According to a first aspect of the present invention, there is provideda solid-state image pickup device that comprises: plural photoelectricconversion elements arranged two-dimensionally, gate portions forreading out signal charges that are photoelectrically-converted in theplural photoelectric conversion elements; plural vertical transferregisters for transferring the signal charges read out through the gateportions in the vertical direction; and first transfer electrodes andsecond transfer electrodes to which driving voltages are applied totransfer the signal charges of the vertical transfer registers,characterized in that the first transfer electrodes are disposed inparallel to the vertical transfer registers, the second transferelectrodes are disposed vertically to the vertical transfer registers,the first transfer electrodes and the second transfer electrodes areformed so as to extend to the upper sides of the gate portions andsupplied with the driving voltages to read out the signal charges fromthe photoelectric conversion elements, so that the signal charges whichare photoelectrically-converted in the photoelectric conversion elementsare read out to the vertical transfer registers by the driving voltagesapplied to both the first transfer electrodes and the second transferelectrodes, the first transfer electrode or the second transferelectrode at the gate portion side of each photoelectric conversionelement and the sensor area of the photoelectric conversion element areformed to be adjacent to each other at a portion where the read-out of asignal charge from the photoelectric conversion element to thecorresponding vertical transfer register is carried out, and an offsetarea is formed between the transfer electrode at the gate portion sideof each photoelectric conversion element and the sensor area of thephotoelectric conversion element at a portion where the read-out of asignal charge from the photoelectric conversion element to thecorresponding vertical transfer register is not carried out.

According to a second aspect of the present invention, there is provideda method of driving a solid-state image pickup device comprising: pluralphotoelectric conversion elements arranged two-dimensionally; gateportions for reading out signal charges photoelectrically-converted inthe plural photoelectric conversion elements, and plural verticaltransfer registers for transferring the signal charges read out by thegate portions in the vertical direction, the vertical transfer registershaving first transfer electrodes and second transfer electrodes thereon,characterized in that a first driving voltage to transfer the signalcharges in the vertical direction are applied to the first transferelectrodes and the second transfer electrodes, and a second drivingvoltage to read out the signal charges from the photoelectric conversionelements are also applied to the first transfer electrodes and thesecond transfer electrodes, whereby the read-out operation of the signalcharges photoelectrically-converted in the photoelectric conversionelements to the vertical transfer registers is carried out on the pluralphotoelectric conversion elements independently every column or/andevery line by the driving voltages applied to both the first transferelectrodes and the second transfer electrodes.

According to the solid-state image pickup device of the presentinvention, the signal charges which are photoelectrically converted inthe photoelectric conversion elements are read out to the verticaltransfer registers by the driving voltages applied to the first transferelectrodes and the second transfer electrodes, whereby a so-called ANDtype solid-state image pickup device is constructed.

Further, the first transfer electrode or the second transfer electrodeat the gate portion side of each photoelectric conversion element andthe sensor area of the photoelectric conversion element are formed so asto be adjacent to each other at the portion where the read-out of thesignal charge to the corresponding vertical transfer register is carriedout, so that the signal charge can be read out between the neighboringsensor area and transfer electrode.

Still further, at the portion where the read-out of the signal charge tothe vertical -transfer register is not carried out, the offset area isformed between the transfer electrode at the gate portion side of eachphotoelectric conversion element and the sensor area of thephotoelectric conversion element, so that no read-out of the signalcharge is carried out at this portion. Therefore, it is discriminated onthe basis of the presence or absence of the offset area whether theread-out of the signal charges is carried out or not.

According to the driving method for the solid-state image pickup deviceof the present invention, the read-out operation is carried out by thedriving voltages applied to both the first transfer electrodes and thesecond transfer electrodes, and thus the so-called AND type operation iscarried out.

Further, the read-out operation of the signal chargesphotoelectrically-converted in the photoelectric conversion elements tothe vertical transfer registers is carried out on the pluralphotoelectric conversion elements independently every column or/andevery line, whereby the accumulation time of the signal charges of thephotoelectric conversion elements is independently varied every columnor/and every line to achieve signals for which the accumulation time isvaried.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the construction (a plan view of the mainpart) of a CCD solid-state image pickup device according to anembodiment of the present invention;

FIGS. 2A to 2C are cross-sectional views taken along A—A, B—B and C—C ofFIG. 1, respectively;

FIG. 3 is a diagram showing an operation based on an SVE system in theCCD solid-state image pickup device of FIG. 1;

FIG. 4 is a diagram (a plan view of the main part) showing theconstruction in which the sensor area of the sensor is extended to thetransfer electrode side in the construction of FIG. 1;

FIG. 5 is a diagram (a plan view of the main part) showing the CCDsolid-state image pickup device according to another embodiment of thepresent invention;

FIG. 6 is a cross-sectional view taken along D—D of FIG. 6;

FIG. 7 is a diagram (a plan view of the main part) showing the CCDsolid-state image pickup device according to another embodiment of thepresent invention;

FIG. 8 is a diagram (a plan view of the main part) showing the CCDsolid-state image pickup device according to another embodiment of thepresent invention; and

FIG. 9 is a diagram (a plan view showing the main part) showing an ANDtype CCD solid-state image pickup device.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, there is provided a solid-stateimage pickup device that comprises a plurality oftwo-dimensionally-arranged photoelectric conversion elements, gateportions for reading out signal charges that arephotoelectrically-converted by the plural photoelectric conversionelements, plural vertical transfer registers for transferring in thevertical direction the signal charges read out by the gate portions; ahorizontal transfer register for horizontally transferring the signalcharges transferred from the plural vertical transfer registers; and atleast first transfer electrodes and second transfer electrodes to whichdriving voltages to transfer the signal charges in the verticaldirection through the vertical transfer registers are applied, whereinthe first transfer electrodes are disposed in parallel to the verticaltransfer registers, the second transfer electrodes are disposedvertically to the vertical transfer registers, the first transferelectrodes and the second transfer electrodes are formed so as to extendto the upper side of the gate portions and supplied with the drivingvoltages to read out the signal charges from the photoelectricconversion elements, so that the signal chargesphotoelectrically-converted in the photoelectric conversion elements areread out to the vertical transfer registers by the driving voltagesapplied to both the first transfer electrodes and the second transferelectrodes, the first transfer electrode or the second transferelectrode at the gate portion side of each photoelectric conversionelement and the sensor area of the photoelectric conversion element areformed to be adjacent to each other at a portion where the read-out ofthe signal charge to the corresponding vertical transfer register iscarried out, and an offset area is formed between the transfer electrodeat the gate portion side of each photoelectric conversion element andthe sensor area of the photoelectric conversion element at a portionwhere the read-out of the signal charge to the corresponding verticaltransfer register is not carried out.

In the solid-state image pickup device of the present invention, anoffset area is also provided between the first transfer electrode andthe second transfer electrode of the vertical transfer registers at theopposite side to the gate portion with respect to each photoelectricconversion element and the sensor area of the photoelectric conversionelement.

In the solid-state image pickup device of the present invention, at theportions where the read-out of the signal charges to the verticaltransfer registers is carried out, the transfer electrodes at the gateportion side of each photoelectric conversion element are formed so asto extend to the sensor area side of the photoelectric conversionelement.

In the solid-state image pickup device of the presents invention, at theportions where the read-out of the signal charges to the verticaltransfer registers is carried out, the sensor area of each photoelectricconversion element is formed so as to extend to the gate portion side.

According to the present invention, there is provided a method ofdriving a sold-state image pickup device comprising a plurality oftwo-dimensionally arranged photoelectric conversion elements, gateportions for reading out signal charges photoelectrically-converted inthe plural photoelectric conversion elements, plural vertical transferregisters for transferring the signal charges read out by the gateportions in the vertical direction, and a horizontal transfer registerfor transferring the signal charges transferred from the plural verticaltransfer registers in the horizontal direction, and at least first andsecond transfer electrodes on the vertical transfer registers, wherein adriving voltage for transferring the signal charges in the verticaldirection is applied to the first and second transfer electrodes, and adriving voltage for reading out the signal charges from thephotoelectric conversion elements is applied to the first and secondtransfer electrodes, whereby the read-out operation of the signalcharges which are photoelectrically-converted by the photoelectricconversion elements to the vertical transfer registers is carried out onthe plural photoelectric conversion elements independently every columnor/and every line by the driving voltages applied to both the first andsecond transfer electrodes.

Prior to the detailed description of preferred embodiments, the summaryof the present invention will be described.

The present invention is applied to a solid-state image pickup devicecomprising plural photoelectric conversion elements (sensors) which aretwo-dimensionally arranged, gate portions for reading out the signalcharges that are photoelectrically-converted by the plural photoelectricconversion elements (sensors), plural vertical transfer registers fortransferring the signals read out by the gate portions in the verticaldirection, and a horizontal transfer register for transferring in thehorizontal direction the signal charges transferred from the pluralvertical transfer registers.

Here, the construction of the solid-state image pickup device describedabove is shown in FIG. 9 (a plan view of the main part of thesolid-state image pickup device).

The CCD solid-state image pickup device shown in FIG. 9 has pluraltwo-dimensionally-arranged photoelectric conversion elements, that is,sensors 11. A transfer electrode 21 formed of a first layer ofpolycrystalline silicon and a transfer electrode 22 (22A, 22B) formed ofa second layer of polycrystalline silicon are disposed at one side ofeach column of the sensors 11, and a vertical transfer register 25 isdisposed at the one side of each column of the sensors 11 in conformitywith the transfer electrodes 21, 22.

Further, a transfer electrode 23 (23A, 23B) of a third layer is disposedon the transfer electrodes 21, 22 of the first layer and the secondlayer in parallel to the vertical transfer register 25.

A gate portion 24 for reading out a signal chargephotoelectrically-converted by each sensor 11 is disposed between thesensor 11 and the vertical transfer register 25 located at the left sideof the sensor 11, and a channel stop area 26 for separating therespective sensor columns from one another is disposed between eachsensor 11 and the vertical transfer register 25 at the right side of thesensor 11.

The signal charge photoelectrically-converted by each sensor 11 is readout through the read-out gate portion 24 to the vertical transferregister 25 at the left side of the sensor 11. The signal charge thusread out is transferred in the vertical direction by the verticaltransfer register 25.

A horizontal transfer register (not shown) for transferring the signalcharge transferred from each vertical transfer register 25 in thehorizontal direction is disposed at the end portion of each verticaltransfer register 25.

Each transfer electrode 21 of the first polycrystalline silicon layercomprises a lead portion which is formed between the sensors 11 arrangedin the vertical direction so as to extend in the horizontal direction,and an electrode portion which downwardly projects along the verticaltransfer register 25 in FIG. 9. Each of the transfer electrodes 22A, 22Bof the second polycrystalline silicon layer comprises a lead portionwhich is formed between the sensors 11 arranged in the verticaldirection so as to extend in the horizontal direction, and an electrodeportion which upwardly projects along the vertical transfer register 25in FIG. 9. The transfer electrode 22A, 22B formed of the secondpolycrystalline silicon layer has an extension portion 22C at the upperside thereof in the vertical direction at the read-out gate portion 24,and the extension portion 22C extends to the upper side of thefirst-layer transfer electrode 21 located just above the transferelectrode concerned.

A first vertical transfer clock φV1 is applied to the transferelectrodes 21 of the first polycrystalline silicon layer, and secondvertical transfer clocks φV2A, φV2B are applied to the transferelectrodes 22A, 22B of the second polycrystalline silicon layer,respectively. Further, third vertical transfer clocks φV3A, φV3B areapplied to the transfer electrodes 23A, 23B of the third polycrystallinesilicon layer, respectively. The vertical transfer operation of thesignal charges is carried out in a three-phase driving mode based onthese vertical transfer clocks by the transfer electrodes 21, 22 (22A,22B), 23 (23A, 23B).

The second vertical transfer clocks φV2A, φV2B and the third verticaltransfer clocks φV3A, φV3B are used to apply not only a driving voltagefor vertically transferring the signal charges in the vertical transferregisters 25, but also a high-level driving voltage for reading out thesignal charges photoelectrically-converted in the sensors 11 to thevertical transfer registers 25.

When, in the read-out gate portion 24, the high-level driving voltage toread-out the signal charges is applied to both of each transferelectrode 22A or 22B of the second polycrystalline silicon layer andeach of the transfer electrode 23A or 23B of the third polycrystallinesilicon layer by the second vertical transfer clock φV2A or φV2B and thethird vertical transfer clock φV3A or φV3B respectively, the signalcharges photoelectrically-converted by the sensors 11 are read out tothe vertical transfer registers 25. That is, a so-called AND type CCDsolid-state image pickup device is constructed.

If the timing at which the high-level driving voltage is applied isvaried between the vertical transfer clock φV2A applied to the transferelectrodes 22A and the vertical transfer clock φV2B applied to thetransfer electrodes 22B, the signal charges of the plural sensors 11could be controlled to be read out independently every line.

Likewise, if the timing at which the high-level driving voltage isapplied is varied between the vertical transfer clock φV3A applied tothe transfer electrodes 23A and the vertical transfer clock φV3B appliedto the transfer electrodes 23B, the signal charges of the plural sensors11 could be controlled to be read out independently every column.

Further, the signal charges of the plural sensors 11 can be controlledto be read out independently every line and every column by combiningthe second vertical transfer clock φV2A, φV2B and the third verticaltransfer clock φV3A, φV3B. Further, by varying the read-out timing of afirst sensor group 11A, a second sensor group 11B a third sensor group11C and a fourth sensor group 11D, the accumulation time can be madedifferent among the respective sensor groups.

That is, the signal charges accumulated in the photoelectric conversionelements can be read out independently every pixel.

In the case of the construction shown in FIG. 9, the extension portion22C at the electrode portion of the transfer electrode 22A, 22B of thesecond layer located at the read-out gate portion 24 is formed to have arelatively small width. The extension portion 22C is required to have awidth to be determined in consideration of the positioning between theextension portion 22C and the transfer electrode 23 (23A, 23B) of thethird layer, etc. Therefore, it is difficult to make each unit cell moreminute (i.e. to design each unit cell in a further microstructure), andthus it is difficult to more enhance a multi-pixel structure or acompact structure for future CCD solid-state image pickup devices.

Therefore, according to the present invention, there is provided asolid-state image pickup device that can perform the same AND typeoperation as the CCD solid-state image pickup device shown in FIG. 9 andalso easily more enhance the microstructure of the unit cell.

FIG. 1 shows the construction of a CCD solid-state image pickup deviceaccording to an embodiment of the present invention (plan view of themain part). FIG. 2A is a cross-sectional view of an arrow of A—A of FIG.1, FIG. 2B is a cross-sectional view of an arrow of B—B of FIG. 1, andFIG. 2C is a cross-sectional view of an arrow of C—C of FIG. 1.

The CCD solid-state image pickup device of this embodiment has aplurality of two-dimensionally arranged photoelectric conversionelements (that is, sensors 11), and vertical transfer registers 25 eachof which is provided at one side of each sensor column.

Transfer electrodes 21 of first polycrystalline silicon layers andtransfer electrodes 22 (22A, 22B) of second polycrystalline siliconlayers are disposed on the vertical transfer registers 25. In conformitywith the transfer electrodes 21, 22, transfer electrodes 23 (23A, 23B)of third layers are disposed in parallel to the vertical transferregisters 25 on the transfer electrodes 21, 22 of the first and secondlayers while each transfer electrode 23 is located at one side of eachsensor column.

A read-out gate portion 24 for reading out a signal chargephotoelectrically-converted by each sensor 11 is disposed between thesensor 11 and the vertical transfer register 25 located at the left sideof the sensor 11, and a channel stop area 26 for separating therespective sensor columns from each other is disposed between eachsensor 11 and the vertical transfer register 25 located at the rightside of the sensor 11 as being hatched in FIG. 1.

The signal charge which is photoelectrically-converted by each sensor 11is read out through the read-out gate portion 24 to the verticaltransfer register 25 located at the left side of the sensor 11. Thesignal charge thus read out is transferred in the vertical direction inthe vertical transfer register 25.

A horizontal transfer register (not shown) for transferring the signalcharge transferred from each vertical transfer register 25 in thehorizontal direction is provided at the end portion of each verticaltransfer register 25.

A first vertical transfer clock φV1 is applied to each transferelectrode 21 of the first polycrystalline silicon layer. Second verticaltransfer clocks φV2A, φV2B are applied to the transfer electrodes 22A,22B of the second polycrystalline silicon layers, respectively. Thirdvertical transfer clocks φV3A, φV3B are applied to the transferelectrodes 23A, 23B of the third polycrystalline silicon layers,respectively. By these vertical transfer clocks, the vertical transferof the signal charges is carried out in the three-phase driving modebased on these vertical transfer clocks by the transfer electrodes 21,22 (22A, 22B), 23 (23A, 23B) of the respective layers.

The second vertical transfer clocks φV2A, φV2B and the third verticaltransfer clocks φV3A, φV3B are used not only to apply the drivingvoltage for vertically transferring the signal charges in the verticaltransfer registers 25, but also to apply the high-level driving voltagefor reading out the signal charges photoelectrically-converted by thesensors 11 to the vertical transfer registers 25.

When, in the read-out gate portion 24, the high-level driving voltagefor reading out the signal charges is applied to the transfer electrodes22A or 22B of the second polycrystalline silicone layers and thetransfer electrodes 23A or 23B of the third polycrystalline siliconlayers by the second vertical transfer clock φV2A or φV2B and the thirdvertical transfer clock φV3A or φV3B respectively, the signal chargeswhich are photoelectrically-converted by the sensors 11 are read out tothe vertical transfer registers 25.

That is, like the CCD solid-state image pickup device shown in FIG. 9,the so-called AND type CCD solid-state image pickup device isconstructed.

As shown in the cross-sectional view of FIGS. 2A to 2C, an N+ impurityregion 2, a P+ positive charge accumulating region 3 and a transferchannel 5 are formed in the neighborhood of the surface of asemiconductor substrate 1.

A photodiode of each sensor 11 is constructed by the N+ impurity region2 and the P+ positive charge accumulating region 3, and each verticaltransfer register 25 is constructed by the transfer channel 5 and thetransfer electrodes 21, 22 and 23 just above the transfer channel 5.

The semiconductor substrate 1 comprises a semiconductor substrate alone,or a combination of a semiconductor substrate and a semiconductorepitaxial layer on the semiconductor substrate.

The channel stop area 26 is constructed by a P type impurity regionformed in the semiconductor substrate 1.

As shown in the cross-sectional view of FIG. 2A, the first-layertransfer electrodes 21, the second-layer transfer electrodes 22 (22A,22B) and the third-layer transfer electrodes 23 (23A) are repetitivelyand alternately disposed so as to be adjacent to the transfer channel 5.

In this embodiment, the construction of the sensor 11, and the transferelectrode 22A, 22B of the second polycrystalline silicon layer and thetransfer electrode 23A, 23B of the third polycrystalline silicon layerlocated at the left side of the sensor 11 at which the read-out gateportion 24 is located is different from that of the CCD solid-stateimage pickup device of FIG. 9.

That is, each transfer electrode 21 of the first polycrystalline siliconlayer is formed between the sensors 11 located in the vertical directionso as to extend in the horizontal direction.

Each of the transfer electrodes 22A, 22B of the second polycrystallinesilicon layer comprises a lead portion extending in the horizontaldirection between the sensors 11 located in the vertical direction, andan electrode portion projecting downwardly in the figure along thevertical transfer register 25. A read-out gate portion 24 is formed atthe electrode portion of the transfer electrode 22A, 22B of the secondpolycrystalline silicon layer.

Each transfer electrode 23A, 23B of the third polycrystalline siliconlayer is formed so as to extend to the sensor 11 at the read-out gateportion 24, and an extension portion 23C thus extending is adjacent tothe sensor 11. That is, as shown in the cross-sectional view of FIG. 2B,the extension portion 23C is formed so as to cover the transferelectrode 22A of the second layer and face the sensor 11, whereby whenthe high-level driving voltage is applied to both the transferelectrodes 22A, 22B of the second layers and the extension portions 23Cof the transfer electrodes 23A, 23B of the third layers, the signalcharges are read out from the sensors 11 to the vertical transferregisters 25 at the read-out gate portions 24.

At the portion other than the read-out gate portion 24 at the left sideof each sensor 11, that is, at the portion 27 where the read-out of thesignal charge is not carried out, the N+ impurity region 2 (hatched inFIG. 1) of each sensor 11 and the transfer electrode 23A, 23B of thethird polycrystalline silicon layer are formed so as to a gaptherebetween, thereby forming an offset area 27A. The P+ positive chargeaccumulating region 3 (dotted in FIG. 1) of each sensor 11 is formedadjacently to the transfer electrode 23A, 23B of the third layer. Thatis, as shown in the cross-sectional view of FIG. 2C, the N+ impurityregion 2 of the sensor 11 is formed so as to be backwardly displacedfrom the transfer electrode 23A, 23B of the third layer, and the offsetarea 27A is formed at the displaced portion between the N+ impurityregion 2 and the transfer electrode 23A, 23B.

The existence of the offset area 27A between the N+ impurity region 2 ofthe sensor 11 (sensor area) and the transfer electrode 23A, 23B of thethird layer prevents the read-out of the signal charges from the sensor11 at this portion 27.

If the timing at which the high-level driving voltage is applied isvaried between the vertical transfer clock φV2A applied to the transferelectrodes 22A and the vertical transfer clock φV2B applied to thetransfer electrodes 22B, the signal charges of the plural sensors 11could be controlled to be read out independently every line.

Likewise, if the timing at which the high-level driving voltage isapplied is varied between the vertical transfer clock φV3A applied tothe transfer electrodes 23A and the vertical transfer clock φV3B appliedto the transfer electrodes 23B, the signal charges of the plural sensors11 could be controlled to be read out independently every column.

Further, the signal charges of the plural sensors 11 can be controlledto be read out independently every line and every column by suitablycombining the second vertical transfer clocks φV2A, φV2B and the thirdvertical transfer clocks φV3A, φV3B.

That is, the signal charges accumulated in the photoelectric conversionelements can be read out independently every pixel.

In the case of FIG. 1, the exposure time can be set independently foreach pixel every repetitive unit of 2 pixels×2 pixels. Accordingly, byvarying the read-out timing of a first sensor group 11A, a second sensorgroup 11B, a third sensor group 11C and a fourth sensor group 11D, theaccumulation time can be varied among the respective sensor groups.

Accordingly, signals can be achieved by each of the sensor groups 11A,11B, 11C, 11D while the exposure time is varied, and an image can bepicked up by using these signals on the basis of a so-called SVE(Spatially Varying exposure), that is, an exposure system of varying theexposure time of each sensor (photoelectric conversion element) withsome patterns every sensor. According to this system, signals for whichthe dynamic range is enhanced can be achieved.

An embodiment of the operation of the SVE system in the CCD solid-stateimage pickup device shown in FIG. 1 will be described with reference toFIG. 3.

In FIG. 3, φSUB shows the driving waveform of a substrate voltage, and11A, 11B, 11C, 11D show the accumulation states of charges of eachsensor of the sensor groups 11A, 11B, 11C, 11D. The charges at hatchedportions in all the charges accumulated are not read out and discardedto the substrate.

First, the substrate voltage φSUB is set to a low level and theaccumulation of charges is started in each of the sensor groups 11A,11B, 11C, 11D.

Subsequently, the high-level read-out voltage is supplied by thevertical transfer clocks φV2B and φV3A, and the signal charges of thethird sensor group 11C connected to the transfer electrodes 22B and thetransfer electrodes 23A are first read out.

Subsequently, the high-level read-out voltage is supplied by thevertical transfer clocks φV2A and φV3B, and the signal charges of thesecond sensor group 11B connected to the transfer electrodes 22A and thetransfer electrodes 23B are read out.

Thereafter, the high-level read-out voltage is supplied by the verticaltransfer clocks φV2A and φV3A, and the signal charges of the firstsensor group 11A connected to the transfer electrodes 22A and 23A areread out.

Finally, the high-level read-out voltage is supplied by the verticaltransfer clocks φV2B and φV3B, and the signal charges of the fourthsensor group 11D connected to the transfer electrodes 22B and thetransfer electrodes 23B are read out. Just after this operation, thesubstrate voltage φSUB is set to a high level, and the charges of thesensors 11 are discharged to the substrate side, whereby the chargesaccumulated in the sensors 11A, 11B, 11C other than the sensors of thefourth sensor group 11D are not read out, but discarded.

As described above, signals are read out from the sensors 11 of the foursensor groups while the exposure time is varied under the followingcondition: 11C<11B<11A<11D.

Further, the signal accumulation time period is overlapped among thefour sensor groups 11, and thus the time displacement can be reduced toa value less than the second method described above, and the dynamicresolution can be more enhanced.

FIG. 3 shows an example of the timing of the vertical transfer clocks,and the timing at which the high-level driving voltage for the read-outin the second and third vertical transfer clocks is applied is notlimited to that of FIG. 3, and it may be set to any timing as occasiondemands.

According to the above-described embodiment, there is provided an ANDtype construction in which the high-level driving voltage for read-outis applied to the transfer electrodes 22 (22A, 22B) of the secondpolycrystalline silicon layers and the transfer electrodes 23 (23A, 23B)of the third polycrystalline silicon layers to read the signal chargesfrom the sensors 11.

By making the timing different between the second vertical transferclocks φV2A, φV2B applied to the transfer electrodes 22A, 22B of thesecond layers or making the timing different between the third verticaltransfer clocks φV3A, φV3B applied to the transfer electrodes 23A, 23Bof the third layers, the signal read-out timing of the sensors 11 may bevaried every other column or every other line.

Accordingly, the exposure time can be set independently for each pixelevery repetitive unit of 2 pixels×2 pixels (four pixels), wherebysignals can be achieved while the accumulation time is changed byvarying the read-out timing of the first sensor group 11A, the secondsensor group 11B, the third sensor group 11C and the fourth sensor group11D, so that the signals for which the dynamic range is enhanced can beachieved. Further, the time displacement of the accumulation time can bereduced, so that the dynamic resolution can be enhanced.

Further, the read-out operation is not carried out in the offset area27A.

Accordingly, the read-out of the signal charges from the sensors 11 tothe vertical transfer registers 25 is carried out at the read-out gateportions 24, and the signal charges are read out to the transferchannels 5 below the electrode portions of the transfer electrodes 22 ofthe second layers.

On the basis of the presence or absence of the extension portion 23C ofthe electrode portion of the transfer electrode 23 of the third layerand the presence or absence of the offset area 27A between the transferelectrode 22, 23 and the sensor area 2 of the sensor 11, the read-outgate portion 24 and the non-read-out portion 27 can be discriminatedfrom each other.

Therefore, it is unnecessary to design the transfer electrodes 23 at theread-out gate portion 24 in a special shape like the construction shownin FIG. 9.

Accordingly, the transfer electrode constituting the read-out gateportion 24, that is, the electrode portion of the transfer electrode 22of the second layer and the extension portion 23C of the electrodeportion of the transfer electrode 23 of the third layer can be formed tohave a relatively large width, and thus it can be designed to have apattern for which the microstructuring can be more easily enhanced.Further, even when it is microstructured, the margin for the positioningcan be kept. Accordingly, even when the unit cell is furthermicrostructured, the further multi-pixel design and the further compactdesign can be implemented for the CCD solid-state image pickup device.

In this embodiment, the extension portion 23C extending to the sensor 11side is formed at the electrode portion of the transfer electrode 23 ofthe third layer, however, any other construction can be used insofar asit enables signal charges to be read out at the read-out gate portions24.

For example, as shown in the plan view of FIG. 4, the transferelectrodes 23 of the third layer may be formed just in the verticaldirection while the sensor areas 2 of the sensors 11 are formed so as toextend to the transfer electrodes 23 of the third layer, therebyconstructing the read-out gate portions 24.

In the case of FIG. 4, at the portions other than the read-out gateportions 24, the N+ impurity region 2 of each sensor 11 does not extendto the transfer electrode 23, and thus an offset area 28 is settherebetween. The signal charges are not read out from the sensor 11 atthis portion by the offset area 28.

Accordingly, as in the case of the construction shown in FIGS. 1 and 2,the high-level driving voltage for readout is applied to the transferelectrodes 22A, 22B of the second layer and the transfer electrodes 23A,23B of the third layer to carry out the read-out operation.

FIG. 5 schematically shows the construction of a CCD solid-state imagepickup device of another embodiment of the present invention (plan viewof the main part), and FIG. 6 is a cross-sectional view of an arrow ofD—D of FIG. 5.

In the CCD solid-state image pickup device of this embodiment, an offsetarea 31 is provided between each column of the sensors 11 and thevertical transfer register 25 at the right side of the sensor column,that is, at the opposite side to the read-out gate portion 24 withrespect to each sensor.

As shown in the cross-sectional view of FIG. 6, the N+ impurity region 2of each sensor 11 is formed so as to be backwardly displaced withrespect to the transfer electrodes 22A, 23A (23B) in the offset area 31.The other construction is the same as the above-described embodiment.The same elements as the above-described embodiment are represented bythe same reference numerals, and the duplicative description is omitted.

According to this embodiment, the offset area 31 is provided betweeneach sensor 11 and the vertical transfer register 25 at the right sidethereof, so that the neighboring columns can be separated from eachother as in the case of the channel stop areas 26 of the aboveembodiment.

Further, the step of forming the P type channel stop areas 26 in thesubstrate 1 is not needed, and thus the number of manufacturing stepscan be reduced.

FIG. 7 schematically shows the construction of a CCD solid-state imagepickup device according to another embodiment (a plan view of the mainpart).

The CCD solid-state image pickup device of this embodiment is achievedby modifying the shape of the electrode portions of the transferelectrodes 22 (22A, 22B) of the second layers of the CCD solid-stateimage pickup device shown in FIG. 1.

The electrode portion of each transfer electrode 22 (22A, 22B) of thesecond layer is formed so as to be wide at the read-out gate portion 24side, narrow at the opposite side to the read-out gate portion 24 andobliquely linear therebetween.

According to this embodiment, the electrode portion of each transferelectrode 22 of the second layer is formed so as to be large in width atthe read-out gate portion 24 side, so that even when the read-outvoltage is reduced, the read-out of the signal charges of the sensors 11can be surely carried out.

By reducing the read-out voltage, the consumption voltage of the CCDsolid-state image pickup device can be reduced, and the electrodeportions and the circuit for supplying the transfer clocks can besimplified in construction.

Further, the electrode portion of each transfer electrode 22 of thesecond layer is formed so as to be small in width at the opposite sideto the read-out gate portion 24, so that the ratio of the area of theelectrode portion of each transfer electrode 22 of the second layer andthe area of the portion at which the transfer electrode 23 of the thirdlayer is not overlapped with the transfer electrode 22 of the secondlayer and faces the transfer channel 5 in the vertical transfer register25 can be set to substantially the same as the construction shown inFIG. 1.

Accordingly, by equalizing the charge amounts to be accumulated belowthe transfer electrodes 21, 22, 23 of the respective layers in thevertical transfer registers 25, the charge amount to be handled by eachvertical transfer register 25 can be prevented from being reduced, andthe charge amount to be handled by each vertical transfer register 25can be set to substantially the same as the construction shown inFIG. 1. Therefore, the other characteristics than the read-out voltagecan be set to substantially the same as the construction shown in FIG.1.

Further, FIG. 8 is a schematic diagram (plan view of the main part) of aCCD solid-state image pickup device of another embodiment of the presentinvention, which is achieved by modifying the shape of the electrodeportions of the transfer electrodes 22 (22A, 22B) of the second layer inthe construction of the CCD solid-state image pickup device shown inFIG. 5 as in the case of the embodiment of FIG. 7.

In the case of the construction shown in FIG. 8, both of an advantagethat the step of forming the channel stop areas shown in FIG. 5 can beomitted and an advantage that the read-out voltage shown in FIG. 7 canbe reduced can be achieved.

In the embodiments shown in FIGS. 7 and 8, the end edge of the electrodeportion of each transfer electrode 22 (22A, 22B) of the second layer isobliquely linearly formed, however, it may be formed in any other shapesuch as a stepwise shape, or a curved line insofar as the requiredcharge amount to be handled by the vertical transfer register 25 can besecured.

In each of the above-described embodiments, the transfer electrodes 21of the first layer are horizontally in a stripe shape. However, in thecase of the construction shown in FIG. 9, the transfer electrode 21 ofthe first layer may be formed so as to extend along the verticaltransfer register 25 so that the width of the electrode portion thereofis larger than that of the lead portion.

Actually, the dimension and interval of the respective transferelectrodes are set so that the charge amounts to be handled by thetransfer electrodes of the respective layers of the vertical transferregister 25, that is, the charge amounts to be handled by the transferelectrodes 21, 22, 23 of the first, second and third Layers are equal toone another.

Further, in the above-described embodiments, there are prepared twokinds of vertical transfer clocks for each of the two-phase verticaltransfer clock (φV2A, φV2B) and the three-phase vertical transfer clock(φV3A, φV3B), however, three or more kinds of vertical transfer clocksmay be prepared to make minute the variation of the read-out timing.

Still further, in the above-described embodiments, the present inventionis applied to the CCD solid-state image pickup device. However, thepresent invention may be applied any other solid-state image pickupdevice insofar as it can transfer signal charges accumulated in eachphotoelectric conversion element (sensor) and then convert the signalcharges to a voltage at the output portion.

The present invention is not limited to the above embodiments, andvarious modifications may be made without departing from the subjectmatter of the present invention.

According to the present invention, on the basis of the presence orabsence of the offset area between the transfer electrode at the gateportion side and the photoelectric conversion element, the gate portionat which the read-out is carried out and the portion where no read-outis carried out can be discriminated from each other, so that it isunnecessary to design the transfer electrodes of the gate portions in aspecial shape. Accordingly, the transfer electrodes can be designed in apattern which is suitable to enhance the microstructure, and the cellsize can be made more minute. Therefore, according to the presentinvention, the multi-pixel and compact design of the solid-state imagepickup device can be enhanced.

Further, according to the present invention, in the solid-state imagepickup device in which the so-called AND type operation is carried out,signals for which the accumulation time is varied can be achieved byvarying the accumulation time of the signal charges of pluralphotoelectric conversion elements independently every column or/andevery line. The accumulation time can be varied and set to any value.

Accordingly, signals for which the dynamic range is enhanced can beachieved. Further, the time displacement of the accumulation time can bereduced and thus the dynamic resolution can be enhanced.

When the offset area is also provided between the first transferelectrode/the second transfer electrode of the vertical transferregister at the opposite side to the gate portion with respect to thephotoelectric conversion element and the sensor area of thephotoelectric conversion element, the step of forming the channel stoparea is not needed, so that the number of manufacturing steps can bereduced.

1. A solid-state image pickup device, characterized by comprising: aplurality of two-dimensionally-arranged photoelectric conversionelements; gate portions for reading out signal charges that arephotoelectrically-converted by said plural photoelectric conversionelements; plural vertical transfer registers for transferring in thevertical direction the signal charges read out by said gate portions;and first transfer electrodes and second transfer electrodes to whichdriving voltages to transfer the signal charges of said verticaltransfer registers are applied, wherein said first transfer electrodesare disposed in parallel to said vertical transfer registers, saidsecond transfer electrodes are disposed vertically to said verticaltransfer registers, said first transfer electrodes and said secondtransfer electrodes are provided so as to contain the upper side of saidgate portions, and the signal charges which arephotoelectrically-converted in said photoelectric conversion elementsare read out to said vertical transfer registers by the driving voltagesapplied to both said first transfer electrodes and said second transferelectrodes, the first transfer electrode or the second transferelectrode at the gate portion side of each photoelectric conversionelement and the sensor area of the photoelectric conversion element areformed to be adjacent to each other at a portion where the read-out ofthe signal charges to each vertical transfer register is carried out,and an offset area, is formed between the transfer electrode at the gateportion side of each photoelectric conversion element and the sensorarea of the photoelectric conversion element at a portion where theread-out of the signal charges to each vertical transfer register is notcarried out.
 2. The solid-state image pickup device as claimed in claim1, wherein a second offset area is provided between said first transferelectrode and said second transfer electrode at the opposite side tosaid gate portion with respect to each photoelectric conversion elementand said sensor area of said photoelectric conversion element.
 3. Thesolid-state image pickup device as claimed in claim 1, wherein at theportions where the read-out of the signal charges to said verticaltransfer registers is carried out, said transfer electrodes at the gateportion side of each photoelectric conversion element are formed so asto extend to the sensor area side of the photoelectric conversionelement.
 4. The solid-state image pickup device as claimed in claim 1,wherein at the portions where the read-out of the signal charges to saidvertical transfer registers is carried out, the sensor area of eachphotoelectric conversion element is formed so as to extend to the gateportion side.